In fabricating semiconductor devices it is often necessary to etch through a layer of insulating material to expose underlying topography such as device regions or contacts. It may be necessary, for example, to etch through a layer of silicon dioxide or glass insulator in order to expose silicon or polysilicon device contacts for subsequent connection to metal. Such etching is typically done with an anisotropic etch process, for example a reactive ion etch (RIE) process using an appropriate plasma etchant.
As device topography becomes increasingly complex, requiring openings of differing widths to features of different heights, the above-described etching processes become increasingly difficult to control. That is, etching tends to continue uncontrollably into the shallower, underlying device features while the process is continued to expose the deeper features. In a similar manner, etching of wider openings tends to progress more quickly than that of narrower openings, also continuing undesirably into the underlying features. This results in damage to the inadvertently etched features.
It is known in the art to use etchants and etch processes which are selective, or preferential, to different materials. U.S. Pat. Nos. 4,465,552, and 4,624,739, for example, show the use of etchants selective to materials overlying silicon or polysilicon. U.S. Pat. Nos. 4,481,706, 4,671,970, 4,668,338, 4,648,937, and 4,455,194 show the use of silicon or polysilicon as an etch stop for an etchant selective to overlying materials. U.S. Pat. No. 4,455,194, for example, shows the forming of a fuse simultaneously with a transistor wherein polysilicon is used as an etch-stop for phosphosilicate glass (PSG).
IBM Technical Disclosure Bulletin Vol. 24, No. 10, March 1982, titled: QUARTZ TRENCH RIE ETCH STOP, to S. Boyar et al., describes the use of both magnesium oxide and metal as an etch stop for quartz.
IBM Technical Disclosure Bulletin Vol. 23, No. 4, September 1980, titled: USE OF OXIDIZED SILICON NITRIDE AS AN ETCH STOP FOR PLASMA ETCHING, to Humphrey, shows the use of silicon oxynitride as an etch stop for polysilicon.
None of the above-described publications, however, are believed to provide etching processes which are sufficiently well-controlled for use with the complex topographies of state-of-the-art semiconductor devices.